Overview of Runoff
- Runoff is often defined as the portion of rain, snowmelt, and irrigation water that moves toward the stream channel rather than infiltrating the soil.
- For some purposes, however, runoff also includes the subsurface water known as interflow which also quickly moves toward the stream channel.
- Runoff is the most important component of flood prediction.
- The three soil water processes are:
- The entry or infiltration of water into the soil
- The transmission of water within the soil
- The storage of water as soil water
- Important runoff terms include:
- Basin – the area that drains to a single outlet point
- Baseflow – the long-term supply that keeps water flowing in streams
- Infiltration – the downward movement of water through the soil surface
- Percolation – the movement of water within the soil profile
- Surface runoff – the movement of water across the soil surface to the stream channel
- Interflow – the relatively rapid movement of water beneath the soil surface to the stream channel
- Runoff – sometimes this is just the surface runoff, but it can refer to a combination of surface runoff and interflow.
- Infiltration rate – the amount of water able to enter the soil in a specified time
- Infiltration capacity – the upper limit of the infiltration rate
- Surface runoff equals the rainfall or snowmelt rate minus the infiltration capacity.
